Optical information recording medium

ABSTRACT

A compound constructed by N (N is an integer of 2 or more) kinds of phases containing at least one kind of elements selected from a group consisting of Co, Ti, V, Cr, Mn, Fe, Ni, Si, Pb, Bi and Al. At least one kind to (N−1) kinds among the N kinds of phases are continuous phases, and the other phases are discontinuous phases.

TECHNICAL FIELD

[0001] The invention relates to an optical information recording mediumand, more particularly, to an optical information recording medium whichcan read out or read/write at a high recording density and has highreliability for the repetitive recording and reproducing operations.

BACKGROUND ART

[0002] In an optical information recording medium, a compact disc (CD),a laser disc (LD), or the like has been widespread. In recent years, aDVD having a recording density that is seven or more times as large asthat of the CD has been put into practical use. As for the DVD,development is being made as a rewritable recording/reproducing mediumbesides a read only ROM (DVD-ROM) in which information has directly beenwritten on a board. The realization of the practical use of the DVD isbeing examined also as an RAM for a computer (DVD-RAM).

[0003] In a DVD, a high density recording has been accomplished by usinga laser beam having a shorter wavelength of about 650 nm than that ofthe laser (780 nm) used in a CD or the like. In order to handleinformation of a large capacity such as computer graphics or the like,however, it is necessary to accomplish a further high recording densitythat is 1.5 to 2 times as large as the above density. To accomplish it,development of semiconductor lasers of green to blue of further shortwavelengths (wavelengths: 520 to 410 nm) is being made.

[0004] A super resolution film can be mentioned as another highrecording density technique. The super resolution film is a film whichis formed on a lower surface of a recording medium and a high recordingdensity can be accomplished by reducing a beam spot of incident lighttransmitted through the film.

[0005] One of mechanisms of a super resolution effect is a saturalabsorption phenomenon which is a phenomenon realized by using suchnonlinear optical characteristics that the super resolution filmtransmits light having an intensity that is equal to or larger than itssatural absorption amount and absorbs light having an intensity belowthe satural absorption amount. Since a spatial intensity of the laserbeam which is used for reading or writing has a Gaussian distribution,when the beam passes through the super resolution film, the light at abottom portion having a low intensity is absorbed by the superresolution film and the light at a center portion having a highintensity is transmitted. Therefore, a beam diameter after thetransmission can be reduced.

[0006] At present, as such a super resolution film, an organic film ofthe phthalocyanine system, materials (compounds) of the chalcogenidesystem, or the like as shown in JP-A-8-96412 or the like can bementioned. Besides them, such a trial that, as the same organicmaterial, a thermochromic material disclosed in JP-A-6-162564 or aphotochromic material disclosed in JP-A-6-267078 is used as a superresolution film is also known.

[0007] However, each of the materials as mentioned above has problems interms of the reliability, productivity, and the like. In the organicfilm, since an energy density of the beam is locally very high uponrecording or reading, if the recording or reproducing operation isrepetitively performed, there is a fear that the film deterioratesgradually. Therefore, it is difficult to guarantee the sufficient numberof times of the recording or reproducing operation under a severe useenvironment as in case of an RAM for a computer or the like. Sincechalcogenide is chemically unstable, it is difficult to obtain a longguaranteeing period.

DISCLOSURE OF INVENTION

[0008] It is an object of the invention to obtain an optical recordingmedium having a super resolution film which can guarantee the repetitiverecording or reproducing operation for a long period and has highproductivity and a high super resolution effect.

[0009] To solve the above problem, according to the invention, there isprovided an optical information recording medium comprising, at least: aboard on which pits having information have been formed; and a filmwhich is formed directly on the board or formed thereon through anotherlayer and changes a reflectance or an intensity distribution ofreflection light in dependence on an intensity of incident light (such afilm is hereinbelow also referred to as a super resolution film),wherein the film is inorganic materials (compounds) constructed by N(N=2, 3, 4, . . . :integer of 2 or more) kinds of phases, the phases ina range from at least one kind to (N−1) kinds among the N kinds ofphases are continuous phases, and the other phases are discontinuousphases.

[0010] The discontinuous phases are, for example, phases such asspherical or pillar fine particles and are phases having such adiscontinuous structure that they are distributed in one matrix. Thecontinuous phases are phases represented by such a matrix phase and arephases all of which are continuous and exist not being independent. Thecontinuous phases exist so as to disperse the discontinuous phases.

[0011] There is also provided an optical information recording mediumcomprising, at least: a board; a film which is formed directly on theboard or formed thereon through another layer and changes a reflectanceor an intensity distribution of reflection light in dependence on anintensity of incident light; and a recording film which is formeddirectly on the film or formed thereon through another layer and onwhich information is recorded by the light, wherein the film isinorganic materials (compounds) constructed by N (N=2, 3, 4, . . .:integer of 2 or more) kinds of phases, the phases in a range from atleast one kind to (N−1) kinds among the N kinds of phases are continuousphases, and the other phases are discontinuous phases. A mean diameterof the discontinuous phases lies within a range from 1 nm or more to 70nm or less. A width of continuous phases existing between thediscontinuous phases lies within a range from 0.3 nm or more to 100 nmor less. Further, the continuous phases are amorphous inorganiccompounds and the discontinuous phases are crystal inorganic compounds.The continuous phases are a dielectric substance and the discontinuousphases are any of a metal, a semiconductor, and a dielectric substance.

[0012] According to the invention, there is provided an opticalinformation recording medium comprising, at least: a board on which pitshaving information have been formed; and a film which is formed directlyon the board or formed thereon through another layer and changes areflectance or an intensity distribution of reflection light independence on an intensity of incident light, wherein the film isconstructed by N (N=2, 3, 4, . . . :integer of 2 or more) kinds ofphases containing at least one or more kinds of elements selected fromCo, Ti, V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a rangefrom at least one kind to (N−1) kinds among the N kinds of phases arecontinuous phases, and the other phases are discontinuous phases.

[0013] Further, there is provided an optical information recordingmedium comprising, at least: a board; a film which is formed directly onthe board or formed thereon through another layer and changes areflectance or an intensity distribution of reflection light independence on an intensity of incident light; and a recording film whichis formed directly on the film or formed thereon through another layerand on which information is recorded by the light, wherein the film isconstructed by N (N=2, 3, 4, . . . :integer of 2 or more) kinds ofphases containing at least one or more kinds of elements selected fromCo, Ti, V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a rangefrom at least one kind to (N−1) kinds among the N kinds of phases arecontinuous phases, and the other phases are discontinuous phases.

[0014] Further, according to the invention, there is provided an opticalinformation recording medium comprising, at least: a board; a film whichis formed directly on the board or formed thereon through another layerand changes a reflectance or an intensity distribution of reflectionlight in dependence on an intensity of incident light; and a recordingfilm which is formed directly on the film or formed thereon throughanother layer and on which information is recorded by the light, whereina refractive index of the film changes due to the incident light whenthe incident light enters, and assuming that a refractive index at thetime when no incident light enters is labelled to no and an intensity ofthe incident light is set to I, if the absolute value-n of therefractive index that is measured is indicated by

n=n ₀ +n ₂ I

[0015] a value of n₂ lies within a range from 1.0×10⁻⁹ (m²/W) or largerto 1.0×10⁻⁷ (m²/W) or less.

[0016] In this instance, the refractive index change (n−n₀) occurs insuch a manner that the refractive index is saturated within a period oftime which lies within a range from 2.50×10⁻⁷ second or longer to3.50×10⁻⁷ second or shorter after the irradiation of the incident lightand is recovered to the original refractive index within a time intervalwhich lies within a range from 2.5×10⁻⁷ second or longer to 1.0×10⁻²second or shorter after the removal of the incident light.

[0017] Further, the film is an oxide which contains a Co oxide of 60 to95 weight % as an oxide of CoO and in which a remaining part isconstructed by elements of at least one or more kinds among Si, Ti, Al,Pb, and Bi.

[0018] According to the invention, there is provided an opticalinformation recording/reproducing apparatus comprising, at least: lasersof a plurality of wavelengths; means for selecting one of the lasers;and a mechanism for automatically adjusting a focal point which changesevery laser, wherein the apparatus further has means for discriminatinga recording capacity of a medium to record or reproduce and means forchanging a tracking in accordance with the medium discriminated by thediscriminating means.

BRIEF DESCRIPTION OF DRAWINGS

[0019]FIG. 1 is a diagram of a cross section of an ROM disk formed in anembodiment of the invention.

[0020]FIG. 2 is a diagram showing a reading frequency dependence of anoutput derived from the ROM disk in FIG. 1.

[0021]FIG. 3 is a diagram showing an X-ray diffraction pattern of asuper resolution film formed in the embodiment of the invention.

[0022]FIG. 4 is a diagram showing an X-ray diffraction pattern of asuper resolution film formed in the embodiment of the invention.

[0023]FIG. 5 is a diagram showing an X-ray diffraction pattern of asuper resolution film formed in the embodiment of the invention.

[0024]FIG. 6 is a photograph showing a TEM image of a super resolutionfilm formed in the embodiment of the invention.

[0025]FIG. 7 is a photograph showing an electron beam diffraction imageof a super resolution film formed in the embodiment of the invention.

[0026]FIG. 8 is a diagram of a cross section of an RAM disk formed inthe embodiment of the invention.

[0027]FIG. 9 is a diagram showing a change in output for a recordingmark length which is obtained from the RAM disk of FIG. 8.

[0028]FIG. 10 is a diagram showing a change in laser beam diameter inthe case where a glass film is formed and in the case where it is notformed.

[0029]FIG. 11 is a diagram showing a relation between the number oftimes of the recording/reproducing operation and an output of the RAMdisk on which a super resolution film in the embodiment of the inventionhas been formed.

[0030]FIG. 12 is a diagram showing a relation between a CoO content andthe output.

[0031]FIG. 13 is a diagram showing a relation between a mean particlediameter of particles precipitated on the film and an output.

[0032]FIG. 14 is a block diagram of an optical informationrecording/reproducing apparatus formed in the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

[0033] The invention will be described in detail by using an embodiment.

[0034]FIG. 1 shows a schematic diagram of a partial ross section of anROM disk formed in the embodiment. In FIG. 1, reference numeral 1denotes a board; 2 a super resolution film; 5 an SiO₂ protecting film; 4a reflecting film made of a material of the Al—Ti system; and 6 a pitwhich has been written with information. Although one of polycarbonate,polyolefin, glass, and the like is used as a board 1 in accordance withthe specification, polycarbonate is used in the embodiment. In FIG. 1,light for reading (for example, laser beam) enters from the lowerposition as shown by an arrow.

[0035] Further, the ROM disk is formed by the following steps. First, apit pattern having information is formed on a photoresist by using alaser. After that, the pit pattern is copied to an Ni die andpolycarbonate is injection formed into the die, thereby forming a board.The super resolution film 2 having a desired film thickness is formed onthe board by sputtering. The SiO₂ protecting film 5 having a filmthickness of 140 nm is formed and, thereafter, the reflecting film 4having a film thickness of 100 nm made of a material of the Al—Ti systemis formed by sputtering. A thickness of board 1 is equal to 0.6 mm. Inthe embodiment, two boards (shown in FIG. 1) formed as films are adheredto each other with a UV (ultraviolet rays) curable resin while thereflecting films 4 are set to the back side, so that an ROM disk havinga thickness of 1.2 mm is obtained. As a film thickness of superresolution film 2, a thickness within a range from 100 nm or more to 300nm or less is selected.

[0036] In the embodiment, by changing compositions (Nos. 1 to 29 inTable 1, which will be explained hereinlater) of the film correspondingto the super resolution film 2, ROM disks (No. 30 in Table 1, which willbe explained hereinlater) are formed and super resolutioncharacteristics of each disk are evaluated. As a comparison example, anROM disk (No. 30 in Table 1, which will be explained hereinlater) onwhich the super resolution film 2 is not formed is also formed. Asputtering apparatus which can simultaneously sputter two disks is usedfor sputtering. The compositions are changed on the films byindependently changing their powers.

[0037]FIG. 14 shows a block diagram of an optical informationrecording/reproducing apparatus used in the embodiment. The apparatushas a medium discriminating means for discriminating the kind of opticaldisk serving as an optical memory medium. An optical disk is fixedtemporarily to a rotating mechanism connected directly or indirectly toa rotary shaft of a motor which is controlled by motor circuit controlmeans. The information on the optical disk is read as a photosignal by alaser serving as a light source in the pickup and a sensing unit forsensing the reflection light. Information is stored onto the opticaldisk by the light source in the pickup. The photosignal passes through apreamplifier, read signal processing means, address reading means, andclock sync signal reading means and is outputted through reproductionsignal demodulating means to the outside of the apparatus byreproduction data sending means. Reproduction data is outputted bypredetermined output means such as display apparatus, speaker, or thelike or is subjected to data processes by an information processingapparatus such as a personal computer or the like.

[0038] In the embodiment, laser selecting means which can select anarbitrary laser wavelength is provided besides a circuit system which isused for normal recording and reproduction. A peak power which is usedis determined by peak power deciding means on the basis of an output ofthe laser selecting means and on the basis of an analysis of a laserpower control information analyzing means. A reading power is similarlydetermined by reading power deciding means. An output of the peak powerdeciding means is inputted to a laser driver via a recording power DCamplifier and an erasing power DC amplifier through power ratio decidingmeans and controls the light source in the pickup. Similarly, an outputof the reading power deciding means is inputted to the laser driverthrough a reading power DC amplifier and controls the light source inthe pickup. As an actual laser, a semiconductor laser of 780 nm which isused for a CD and semiconductor lasers of 650 nm, further, 520 nm, and410 nm which are used for a DVD are installed.

[0039] Since a focus and a focal depth differ depending on a wavelength,the laser is designed so as to have such a structure that anauto-focusing can be performed in association with the selection.Further, in correspondence to a structure in which a super resolutionfilm is mounted on the disk and a tracking width is made thin, intracking error detecting means, another means for high density recordingis separately provided, thereby enabling the tracking operation to beperformed in accordance with a medium. A kind discriminating mechanismfor discriminating the medium by using a difference of reflectance ofmedia is provided, thereby designing the apparatus so that theauto-tracking can be performed in accordance with a difference of themedium kinds. Upon data recording, recording data is inputted fromrecording data receiving means, is data modulated by recording datamodulating means, is inputted to the laser driver through recordingtiming correcting means, and controls the light source in the pickup.

[0040] By using a construction as shown in FIG. 14, not onlyconventional CD and DVD can be compatibly used but also disks havingdifferent recording capacities due to the realization of a largecapacity can be handled by one apparatus. The optical informationrecording/reproducing apparatus can be properly changing itsconstruction in accordance with its object or application field andused.

[0041] Table 1 shows reproduction output characteristics of compositionsof the films corresponding to the formed super resolution films and alow frequency component (2 MHz) and a high frequency component (10 MHz)under such conditions that a reading power is set to 1, 2, 3, and 4 mW.The presence or absence of the super resolution effect to bediscriminated from this table is also shown. The laser beam used forreading is derived from the semiconductor laser of a wavelength of 650nm. TABLE 1 Nonlinear Output refractive Response Super Components 2 MHz10 MHz index time resolution No. (weight ratio) 1 mW 2 mW 3 mW 4 mW 1 mW2 mW 3 mW 4 mW (n₂(m²/w) (ns) effect 1 CoO 34 35 35 33 1 2 2 1 2.5 ×10⁻¹⁵ 140 X 2 SiO₂ 38 40 41 40 1 2 2 2 3.4 × 10⁻¹⁸ 125 X 3 SiO₂:CoO =1:1 35 36 36 37 2 3 3 2 6.2 × 10⁻¹² 210 X 4 SiO₂:CoO = 1:2 43 44 45 4710 13 20 25 2.7 × 10⁻⁸ 330 ◯ 5 SiO₂:CoO = 1:3 39 40 45 42 17 19 23 285.4 × 10⁻⁸ 345 ◯ 6 SiO₂:CoO = 1:4 38 35 38 40 20 25 30 35 7.4 × 10⁻⁸ 350◯ 7 SiO₂:CoO = 1:9 38 38 39 38 22 27 32 38 1.0 × 10⁻⁷ 350 ◯ 8 Glass 3639 32 37 1 2 2 3 6.3 × 10⁻¹⁷ 180 X 9 Glass:CoO = 1:1 37 38 40 41 5 4 8 95.9 × 10⁻¹² 220 X 10 Glass:CoO = 1:2 35 38 39 38 12 15 21 29 3.3 × 10⁻⁸300 ◯ 11 Glass:CoO = 1:3 37 38 38 37 17 20 22 28 5.9 × 10⁻⁸ 320 ◯ 12Glass:CoO = 1:4 38 39 41 40 20 25 29 32 1.1 × 10⁻⁷ 350 ◯ 13 TiO₂ 35 3636 35 1 2 3 3 1.0 × 10⁻¹¹ 200 X 14 TiO₂:CoO = 1:1 37 36 35 37 2 3 4 62.9 × 10⁻¹⁰ 195 X 15 TiO₂:CoO = 1:2 35 37 38 40 15 16 18 22 9.2 × 10⁻⁹250 ◯ 16 TiO₂:CoO = 1:3 36 38 39 40 15 18 19 21 2.2 × 10⁻⁸ 310 ◯ 17TiO₂:CoO = 1:4 37 35 38 39 18 19 22 28 6.7 × 10⁻⁸ 345 ◯ 18 Al₂O₃ 39 3837 38 2 3 2 2 2.3 × 10⁻⁸ 155 X 19 Al₂O₃:CoO = 1:1 39 40 38 39 14 15 1820 1.0 × 10⁻⁸ 325 ◯ 20 Al₂O₃:CoO = 1:2 40 41 41 40 15 17 19 23 2.5 ×10⁻⁸ 335 ◯ 21 Al₂O₃:CoO = 1:3 35 36 38 38 17 18 20 25 1.0 × 10⁻⁸ 350 ◯22 SiO₂—PbO 35 37 37 38 10 12 13 15 9.4 × 10⁻⁹ 280 ◯ 23 (SiO₂—PbO):CoO =1:1 38 38 39 41 17 18 20 25 2.2 × 10⁻⁸ 350 ◯ 24 (SiO₂—PbO):CoO = 1:2 3938 37 38 22 25 28 30 6.5 × 10⁻⁸ 360 ◯ 25 (SiO₂—PbO):CoO = 1:4 40 41 4140 25 26 30 34 3.0 × 10⁻⁸ 345 ◯ 26 SiO₂—Bi₂O₃ 36 35 37 36 12 13 15 168.8 × 10⁻⁹ 310 ◯ 27 (SiO₂—Bi₂O₃):CoO = 1:1 37 37 38 37 18 19 22 25 6.2 ×10⁻⁸ 340 ◯ 28 (SiO₂—Bi₂O₃):CoO = 1:2 38 39 38 38 21 23 24 28 4.0 × 10⁻⁸325 ◯ 29 (SiO₂—Bi₂O₃):CoO = 1:4 37 38 36 37 20 22 23 25 2.1 × 10⁻⁸ 315 ◯30 None 38 41 43 41 1 2 3 5 2.7 × 10⁻²⁰ 120 X

[0042] In the embodiment, to obtain a higher super resolution effect, afilm containing the Co oxide showing large absorption at wavelengthsaround 650 nm is used as a base and various materials are added, therebyforming films. In Table 1, compositions are shown by a weight ratio ofeach component. In Table 1, No. 1 shows a single-phase film of CoO andNo. 2 shows a single-phase film of SiO₂. Nos. 3 to 7 indicate filmsformed by using two films of SiO₂ and CoO as targets and adjusting asputtering power of each target. Similarly, No. 8 shows a film formed bymixing a soda-lime glass of the SiO₂—Na₂O—CaO—MgO—Al₂O₃ system. Nos. 9to 12 indicate films formed by mixing the soda-lime glass and CoO. No.13 indicates a TiO₂ single layer film. Nos. 14 to 17 denote mixturefilms by mixing CoO and TiO₂.

[0043] Further, Nos. 18 to 21 show mixture films of the Al₂O₃ system andCoO. Nos. 22 to 25 show mixture films of the SiO₂—PbO glass system andCoO. Nos. 26 to 29 show mixture films of a single layer film of theSiO₂—Bi₂O₃ glass system and CoO. In those glass systems, glass blocks ofthe SiO₂—PbO system and the SiO₂—Bi₂O₃ system are previously formed andused as targets, thereby forming the films. No. 30 relates to an examplein which the super resolution film 2 is not formed.

[0044] In FIG. 2, the frequency dependence of reproduction outputcharacteristics was analyzed by a spectrum analyzer. A measurementexample of the reproduction output characteristics by the spectrumanalyzer is shown. In FIG. 2, the formed film is the film of No. 4 inthe embodiment. A measurement example in the case (No. 30) where no filmis formed is also shown as a comparison example. Both reproducing laserpowers are equal to 1 mW.

[0045] In the case where the film of No. 4 in the embodiment is formedas a super resolution film, it has been found that an output level ishigh up to a higher frequency component than that in the case where nosuper resolution film is formed (No. 30). Since the high frequencycomponent of the signal is drawn on the ROM disk by a denser pitpattern, in the case where the super resolution film is formed, thismeans that a finer pit pattern is read out and a reproduction signal isoutputted. Thus, in the case where the super resolution film of No. 4 isformed, the super resolution effect is obtained.

[0046] Upon discrimination of the super resolution effect in Table 1,outputs at 2 MHz and 10 MHz in each reproduction output are read outfrom a spectrum as shown in FIG. 2. The case where the output at 10 MHzas a high frequency signal is equal to or higher than 10 dB is set to“o” by regarding that there is the super resolution effect. The casewhere it is lower than 10 dB is determined by setting it to “x”.

[0047] In the case where the super resolution film is not formed likeNo. 30 in Table 1, as shown in FIG. 2, although a relatively high outputis obtained at a low frequency of 2 MHz, a sufficient output is notobtained at a high frequency of 10 MHz and it has been found that datain this frequency region cannot be read out.

[0048] In the CoO—SiO₂ system of Nos. 1 to 7, reproduction outputs at ahigh frequency are low and the super resolution effect cannot beobtained in case of the CoO single-phase film of No. 1 and the SiO₂single-phase film of No. 2 and in the case where the (SiO₂:CoO) ratio ofNo. 3 is equal to (1:1). In cases of Nos. 4 to 6 in which the content ofCoO exceeds 60%, the high frequency component is also reproduced as ahigh output and the super resolution effect is obtained.

[0049] In the CoO-soda-lime glass system of Nos. 8 to 12, in a mannersimilar to the cases of Nos. 2 to 6, although the super resolutioneffect cannot be obtained in case of the glass single-phase film of No.8 and in case of the (glass:CoO) ratio=(1:1) of No. 9, the superresolution effect can be obtained in cases of Nos. 10 to 12 in which theCoO content is large.

[0050] Even in the TiO₂—CoO system films of Nos. 13 to 17, in a mannersimilar to the embodiment, although the super resolution effect cannotbe obtained in case of the TiO₂ single-phase film (No. 13), the superresolution effect can be obtained in Nos. 13 to 17 in which a largeamount of CoO is contained. Similarly, in the Al₂O₃—CoO system of Nos.18 to 21, although the super resolution effect is not obtained in theAl₂O₃ single-phase film, the super resolution effect can be obtained byallowing a large amount of CoO to be contained in this film.

[0051] In the (SiO₂—PbO)—CoO system of Nos. 22 to 25 and the(SiO₂—Bi₂O₃)—CoO system film of Nos. 26 to 29, the super resolutioneffect can be obtained even in the case where CoO is not contained. Ithas been found that by allowing CoO to be contained therein, an outputat a high frequency is large and the very excellent super resolutioneffect is obtained.

[0052] From the above results, it has been found that the high superresolution effect can be obtained irrespective of the components of thematrix such as SiO₂, glass, TiO₂, or the like if CoO of the content ofabout 65% or more is contained. Therefore, a relation between the superresolution effect and the CoO content is examined from the output of thehigh frequency component of 10 MHz at the time when SiO₂ is used as amatrix component and the CoO content is increased.

[0053]FIG. 12 shows an output dependence of the ROM disk for the CoOcontent (weight ratio). The laser wavelength is set to 650 nm and thelaser output is set to 2 mW. As shown in FIG. 12, it has been found thatin a region of a small CoO content, the output is equal to 1 to 2 dB andis low and the super resolution reproduction is not performed. It hasbeen found that the output gradually increases from a point where theCoO content is equal to about 60 weight % and a relatively high outputof about 10 to 20 dB is obtained in a range where the CoO content isequal to up to 95 weight %. However, it has been found that if the CoOcontent exceeds 95 weight %, the output drops suddenly and the superresolution effect is not obtained.

[0054] As mentioned above, to obtain the high super resolution effect,it is desirable that the CoO content (when the Co oxide is calculated asan oxide of CoO) lies within a range from 60 weight % or more to 95weight % or less irrespective of the kind of matrix.

[0055] As mentioned above, in the film having the high super resolutioncharacteristics, as shown in Table 1, the reflection light intensity(corresponding to the output), namely, the reflectance is largelychanged in dependence on the incident light intensity. As will beexplained hereinlater, the reflection intensity of the beam which wasreflected by the reflecting film and returned after it had beentransmitted through the film does not have a Gaussian distribution uponentering and a deviation occurs in the intensity distribution. From theabove results, it has been found that the high super resolution effectis obtained by providing the film in which the reflectance of thereflection light is changed or the intensity distribution is changed independence on the intensity of the incident light.

[0056] As shown in Table 1, the nonlinear refractive index and theresponse time of the refractive index change of each film aresubsequently evaluated. The evaluation of those optical characteristicsis made by using a Z-scan method whereby the film is formed on a glassboard, a laser beam of 650 nm is vertically inputted onto the filmsurface, a sample is scanned in the optical path direction of theincident light, and a peak intensity of the laser is plotted. Anonlinear refractive index n₂ is calculated by using the followingequation.

n=n ₀ +n ₂ I

[0057] where, n denotes the refractive index to be observed, n₀indicates the refractive index which does not depend on the intensity oflight, and I shows the intensity of the incident light (W/m²).Therefore, the larger the value of n₂ is, the larger the intensitydependence of the refractive index on the light is, and the materialscan be regarded as excellent nonlinear optical materials.

[0058] The response time is evaluated by a method whereby pulse light onthe order of AL second is irradiated as an excitation light, pulse lighton the order of nanosecond is inputted as reading light, the refractiveindex is measured, and a change in refractive index in the pulse lightis plotted for the time. A time that is required from a point when theexcitation light enters until a point when the refractive index changesand is saturated is calculated and used as a response time.

[0059] By first comparing the refractive index change amount n₂, it hasbeen found that n₂ of the materials by which the super resolution effectappeared lies within a range of 10⁻⁹ to 10⁻⁷. It has been also foundthat in case of the materials whose n₂ is equal to or less than9.0×10⁻¹⁰, no super resolution effect is derived. From the aboveresults, in order to obtain the super resolution effect, it is necessaryto set the nonlinear refractive index n₂ to be equal to or larger than1.0×10⁻⁹ (m²/W). If the refractive index change amount is too large,such a phenomenon that the incident light does not reach the recordingfilm appears. When it is examined in detail, if n₂ exceeds 1.0×10⁻⁵(m²/W), the incident light does not reach the recording film and cannotbe detected by the photosensing system.

[0060] By the above examination, it is preferable that the nonlinearrefractive index n₂ lies within a range from 1.0×10⁻⁹ (m²/W) or largerto 1.0×10⁻⁵ (m²/W) or less.

[0061] The faster the response time of the film is, the larger therefractive index change is obtained even if the medium is rotated at ahigh speed. It has been found that the larger the nonlinear refractiveindex n₂ is, the longer the response time is. Although the response timechanges within a range from 120 nsec to 360 nsec, when the film by whichthe super resolution effect can be obtained is examined, it has beenfound that it is sufficient that the response time is equal to orshorter than 350 nsec. If the response time is equal to or shorter thanthat value, even if the nonlinear refractive index is large, theresponse time is slow, so that the apparent refractive index changeamount decreases. If the response time is too fast contrarily, since therefractive index successively changes during the irradiation of thelaser beam, the refractive index is returned to the initial valueaccording to circumstances. There is, consequently, a problem that therefractive index change amount decreases. According to the embodiment,if the response time is equal to or longer than 250 nsec, a decrease inrefractive index change amount does not appear. By the aboveexamination, it is desirable that the response time lies within a rangefrom 250 nsec (2.50×10⁻⁷ second) or longer to 350 nsec (3.50×10⁻⁷second) or shorter.

[0062] As for an optical information recording medium as a rotatingmember in which a disk rotates, it has been found that in the case wherea portion to be irradiated has been recovered to the original refractiveindex until the disk is rotated once, the information can be reproducedat a high S/N ratio. By examining the recovery time in detail, goodresults are obtained in a film which is recovered for a period of timewithin a range from 250 nsec or longer to 10 msec or shorter. If therecovery time is shorter than 250 nsec, since the foregoing responsetime is also shortened in such a film, the refractive index changeamount substantially decreases. If the recovery time exceeds 10 msec,the refractive index is not recovered until the disk is rotated once anda good super resolution effect is not obtained. From the above results,it is desirable that the recovery time lies within a range from 250 nsec(2.5×10⁻⁷ second) or longer to 10 msec (1.0×10⁻² second) or shorter.

Embodiment 2

[0063] To subsequently examine a film structure that is effective toobtain the super resolution effect, the film structure of each superresolution film is analyzed by an X-ray diffraction, a transmissionelectron microscope, and an energy dispersive X-ray spectroscopy. In theembodiment, the film structure of No. 4 by which the super resolutioneffect was obtained and the film structure of Nos. 1 and 2 by which nosuper resolution effect was derived are analyzed.

[0064]FIG. 3 shows an X-ray diffraction pattern of the film of No. 2 asa comparison example. From this diagram, it has been found that a cleardiffraction peak does not appear in the film of No. 2 and this film isamorphous.

[0065]FIG. 4 shows an X-ray diffraction peak of the film of No. 4. Asshown in FIG. 4, a peak indicative of the existence of a crystal appearswhile a halopattern which is obtained from the board is used as abackground. From the obtained peak, it is possible to decide that theprecipitated crystal is CoO. To examine a fine structure of this film indetail, the film structure is evaluated by the transmission electronmicroscope.

[0066]FIG. 6 is a photograph showing a plane TEM image of the film ofNo. 4. As shown in the photograph of FIG. 6, it has been found that thefilm of No. 4 is a set of fine particles having a particle diameter ofabout 10 nm. It has also been found that a grain boundary phase having awidth of about 1 nm exists in the grain boundary portion. It has beenfound that the grain boundary phase is grown in a state to surround theparticles and the grain boundary phase itself forms mesh-like continuousphases. It has been found that the crystal particles are mutually andspatially separated by the continuous phases and become thediscontinuous phases. It has, therefore, been found that the film of No.4 is inorganic materials (compounds) constructed by two kinds of phases,one of the two kinds of phases is the continuous phases, and the otherphases are the discontinuous phases.

[0067] A similar examination is made for the film of No. 23 in Table 1.It has been found that the film of No. 23 is inorganic compoundsconstructed by three kinds of phases, one kind among the three kinds ofphases is the continuous phases containing Si, and the other two kindsof phases are the two kinds of discontinuous phases containing Co andPb.

[0068] Subsequently, FIG. 7 is a photograph showing a selected areaelectron diffraction pattern of the film of No. 4. Many spots areobserved at several portions of a d value in the photograph. From theseresults, it has been found that the particles are crystal gain. Aslightly bright halo is observed inside of a ring constructed by thosespots. Since amorphous constructing this halopattern is not observed inthe particles, it is possible to decide that the grain boundary phase isamorphous.

[0069] From the above results, it has been found that the film of No. 4is a set of fine crystal gain having a mean particle diameter of about10 nm surrounded by the amorphous grain boundary phases.

[0070]FIG. 5 shows an X-ray diffraction pattern of the film of No. 1. Asshown in the diagram, a very clear crystalline peak is observed. Thispeak corresponds to CoO and Co₃O₄. When a fine structure of this film isevaluated by the TEM, a particle diameter is equal to about 0.1 μm. Theexistence of the amorphous phase as shown in the photograph of FIG. 6 isnot observed in the grain boundary portion. From the above results, ithas been found that the halopattern seen in the X-ray diffractionpattern of FIG. 5 is caused due to the glass board and the film of No. 1is constructed only by a crystal.

[0071] From the results of the fine structure analysis and the resultsof the recording and reproducing characteristics shown in Table 1mentioned above, it has been found that the necessary super resolutioneffect cannot be derived if the film is the continuous phases such asperfect amorphous or the continuous phases as a perfect crystal. It hasbeen found that a high super resolution effect can be obtained if thefilm has such a structure that the crystal particles (discontinuousphases) having a particle diameter on the order of nanometer aresurrounded by the amorphous continuous phases like a film of No. 4.

[0072] An influence which is exerted on the super resolution effect bythe existence state of the fine particles is subsequently examined. Inthe examination, the film of No. 4 is formed as a super resolution filmby using a glass board as a board.

[0073] The particle diameter of the particles which are formed can becontrolled by controlling a board temperature upon film formation. Filmshaving various particle diameters are formed by using the aboveprinciple and the super resolution effect is examined. The examinationof the super resolution effect is made by evaluating the output of thehigh frequency component shown in FIG. 2.

[0074]FIG. 13 shows a change in output for a mean particle diameter (nm)of the fine particles observed in the film of No. 4. As shown in thediagram, in the case where the mean particle diameter of the fineparticles is equal to 0.8 nm, the high frequency output is notsufficiently obtained and an output level is the same as that in case ofthe amorphous. When the mean particle diameter of the fine particles isequal to 1.2 nm, the output is equal to 15 dB and is improved largely.When the mean particle diameter of the fine particles lies within arange from 5 nm or larger to 50 nm or less, the output is equal to about28 dB and a relatively large value is obtained.

[0075] It has been found that, when the mean particle diameter of thefine particles is further increased, the output decreases from a pointwhere it is equal to about 60 nm and, when the mean particle diameter isequal to 70 to 90 nm, the output is reduced to a small level on theorder of one digit. It is considered that this is because as the meanparticle diameter of the fine particles increases, the effect ofdispersion of the light increases and a light amount to be detecteddecreases.

[0076] From the above results, to obtain the super resolution effect, itis desirable that the mean particle diameter of the precipitatedparticles lies within a range from 1 nm or more to 70 nm or less. Toobtain the higher super resolution effect, it is desirable that theparticle diameter of the fine particles lies within a range from 5 nm ormore to 50 nm or less.

[0077] If the discontinuous phases surrounding the particles do notexist either, no super resolution effect is derived. Even if the film isconstructed only by the perfect amorphous phases, no super resolutioneffect is derived. By the above examination, the relation between thethickness of continuous phases existing between the particles and thesuper resolution effect is checked, so that the high super resolutioneffect is not obtained if the width of continuous phase between theparticles is less than 0.3 nm. It has been found that, when thecontinuous phase width lies within a range from 0.3 nm or larger to 100nm or less, the super resolution effect can be obtained. Thus, it hasbeen found that, when the continuous phase width increases and theparticle diameter of the fine particles relatively decreases, it iscontrarily difficult to obtain the super resolution effect.

[0078] From the above results, although the continuous phases have toexist, it is desirable that the continuous phase width lies within arange from 0.3 nm or more to 100 nm or less.

[0079] If the continuous phases are an insulating substance (dielectricsubstance) of inorganic materials having a wide band gap, excellenttranslucent performance is obtained and a sufficient reflectionintensity is obtained. Further, when the continuous phases are amorphousinorganic compounds, further better translucent performance is obtained.If the continuous phases are a dielectric substance, the fine particlesas discontinuous phases do not disperse the light even if they are asemiconductor or metal so long as the particle diameter is sufficientlysmaller than a wavelength of laser to be used, specifically speaking, solong as it is equal to or shorter than {fraction (1/10)} of a wavelengthto be used for measurement. The light is influenced by a dipole ofelectrons which are excited in the fine particles by the light energyand the super resolution effect can be obtained.

[0080] Even in the case where the formed fine particles are inorganiccompounds of an insulating substance as mentioned in the embodiment, ifan exciting state is formed because electrons in the compounds areexcited by the light and the refractive index or the like of the film ischanged, the super resolution effect can be obtained.

[0081] The above embodiment has been mentioned with respect to the casewhere the laser wavelength is set to 650 nm and with respect to thesystem containing Co. However, it has been found that, according to thisCo oxide, good super resolution characteristics can be obtained inalmost the whole band of the visible light. It has been found that asimilar effect can be obtained also in the case where V, Cr, Mn, Fe, orNi as another transition metal element is allowed to be contained.

Embodiment 3

[0082] An RAM disk constructed by forming the film examined as mentionedabove onto the board is subsequently formed and its characteristics areevaluated. FIG. 8 is a diagram showing a partial cross section of theRAM disk formed in the embodiment. In FIG. 8, reference numeral 1denotes the board, 2 the super resolution film, 3 the recording film, 4the reflecting film, and 5 and 85 protecting films. An arrow in thediagram indicates an entering direction of light (for example, laserbeam) for recording or reproduction. In the embodiment, a disk-shapedboard having a thickness of 0.6 mm and a diameter of 120 mm is used as apolycarbonate board of the board 1. The super resolution film 2 having athickness of 300 nm is formed on the board 1 by a sputtering method. AZnS—SiO₂ protecting film having a thickness of 80 nm is formed on thefilm 2. After that, a Ge—Sb—Te system phase change film serving as arecording film having a thickness of about 20 nm is likewise formed bythe sputtering method. After the formation of the protecting film ofabout 90 nm, an AlTi reflecting film having a thickness of about 200 nmis further formed. In a manner similar to the case of the ROM disk, twoboards on each of which the films shown in FIG. 8 have been formed areadhered to each other with a UV curable resin in a state where thereflecting films 4 are set to the back side, thereby obtaining a desiredRAM disk.

[0083] In the embodiment, the film having the same compositions as thosein the film of No. 4 in Table 1 is used as a super resolution film. AnRAM disk on which no super resolution film is formed is also formed as acomparison example.

[0084]FIG. 9 shows a reproduction output intensity of the RAM disk onwhich recording marks having the same shape have been formed at regularintervals for a mark length of the recording marks. A reading laserpower is set to 2 mW. It has been found that the reproduction output inthe case where the super resolution film having the same compositions asthose in the film of No. 4 has been formed is higher than that of thecomparison example in which no super resolution film is formed (withoutsuper resolution film in FIG. 9) with respect to a short mark length. Ithas, therefore, been found that in the case where the super resolutionfilm has been formed, the output can be reproduced with respect to theshorter mark length. From this result, the super resolution effect canbe confirmed also for the RAM disk.

[0085] By examining all of the super resolution films in Table 1,results similar to those in case of the ROM disk are obtained.

[0086] Subsequently, a space intensity distribution of the reflectionlight when the above super resolution effect has been obtained isexamined. FIG. 10 shows a diagram of intensity distributions of thelaser beam for the progressing direction of the beam in the case wherethe film has been formed and the super resolution effect has beenobtained and the case where no super resolution film is formed. Theintensity distribution upon entering shows a Gaussian distribution. Ithas been found that, when no super resolution film is formed, a spacedistribution intensity 101 of the reflection light almost shows theGaussian distribution, and that when the super resolution film isformed, a space distribution intensity 102 of the reflection light showsa state where the distribution of the beam is deviated in theprogressing direction. At the same time, it has been found that a beamdiameter Q′ at a beam intensity necessary to read out is smaller than abeam diameter Q necessary to read out in the case where no superresolution film is formed.

[0087] As mentioned above, by forming the super resolution filmaccording to the embodiment, the intensity or intensity distribution ofthe reading light can be changed. The super resolution effect can beobtained in such a case.

[0088] Subsequently, wavelength dependence of the super resolutioneffect is examined. The wavelength dependence is examined by a methodwhereby an RAM disk similar to that of FIG. 8 is formed, an output forthe mark length similar to that in FIG. 9 is obtained with respect toeach wavelength, and the minimum value (1 m) of the mark length at whichthe output is equal to or larger than 30 dB is examined. Lasers of 410nm (blue), 520 nm (green), and 650 nm (red) are used as laser beams.

[0089] Results are shown in Table 2. In case of any of films, it hasbeen found that the minimum value 1 m of the mark length at which theread output is equal to or larger than 30 dB decreases as the wavelengthis shorter. This is because, in case of using the same optical lens, theshorter the wavelength is, the smaller the converged spot diameter is,and even a small mark can be reproduced. TABLE 2 1 m (μm) No. 410 nm 520nm 650 nm 4 0.19 0.24 0.30 5 0.19 0.24 0.30 6 0.17 0.22 0.28 7 0.17 0.220.28 10 0.19 0.24 0.30 11 0.19 0.24 0.30 12 0.17 0.22 0.28 15 0.19 0.240.30 16 0.19 0.24 0.30 17 0.19 0.24 0.30 19 0.19 0.24 0.30 20 0.19 0.240.30 21 0.19 0.24 0.30 22 0.21 0.26 0.32 23 0.19 0.24 0.30 24 0.17 0.220.28 25 0.17 0.22 0.28 26 0.21 0.26 0.32 27 0.19 0.24 0.30 28 0.19 0.240.30 29 0.19 0.24 0.30 30 0.25 0.32 0.40

[0090] With respect to the RAM disk on which the film by which the superresolution effect was obtained in Table 1 has been formed, it has beenfound that the minimum value 1 m (μm) of the mark length is small at anyof the wavelengths. It has, consequently, been found that by forming thefilm, the readable mark length can be reduced multiplicatively by boththe realization of the short laser wavelength and the super resolutioneffect.

Embodiment 4

[0091] Deterioration of the film for the repetitive reproduction issubsequently examined. Evaluation is performed by repetitivelyirradiating the reproduction signal light to the formed RAM disk anddetecting its reproduction output. A mark length of the recording marksis set to 0.3 μm. A film having the same compositions as those in thefilm of No. 4 in Table 1 is used as a super resolution film. Further, aphthalocyanine system organic film is selected as a comparison exampleand is similarly examined.

[0092]FIG. 11 shows an output for the number of repeating times. In caseof the disk on which the phthalocyanine system organic film has beenformed, it has been found that the output gradually decreases from apoint corresponding to the number of repeating times that is slightlysmaller than 10,000 times. In case of the disk on which a glass filmconstructed by inorganic compounds having the same compositions as thosein the film of No. 4 in Table 1 according to the embodiment has beenformed, the output hardly decreases even by the repetitive reproductionof 100,000 times. As mentioned above, according to the optical disk ofthe embodiment, it has been found that the super resolution effect isheld even after completion of the repetitive reproduction.

[0093] A high stability can be obtained for the repetitive reproductioneven in the case where the films by which the super resolution effecthas been derived in the embodiment 2 (in Table 1, Nos. 5 to 7, Nos. 10to 12, Nos. 15 to 17, Nos. 19 to 29) among the other glass films inTable 1 are used as glass films.

[0094] As shown above, according to the embodiment, a read only opticaldisk (ROM disk) of a large capacity in which, further, a degree ofdeterioration is small for the repetitive reading operation is obtained.A large capacity rewritable optical disk (RAM disk) in which adeterioration is small for the repetitive reading and writing operationsis obtained. Further, according to the embodiment, since an oxide suchas transition metal or the like is contained in the glass board, a largecapacity read only optical disk (ROM disk) can be obtained by themanufacturing based on the ordinary optical disk manufacturing steps.According to the embodiment, a large capacity rewritable optical disk(RAM disk) can be obtained by the manufacturing based on the ordinaryoptical disk manufacturing steps.

[0095] According to the invention, an optical recording medium havingthe super resolution film in which an output deterioration is small evenif the reproduction is repetitively performed or the recording andreproduction are repetitively performed can be obtained.

[0096] According to the invention, an optical recording medium havingthe super resolution film in which good productivity is obtained andwhich has the super resolution effect can be obtained.

Industrial Applicability

[0097] The optical information recording medium according to theinvention is generally called an optical disk and, particularly, a superresolution film which can be used as an optical disk on/from whichinformation can be recorded/reproduced and can record/reproduceinformation at a high density and has the high super resolution effectcan be provided.

What is claimed is:
 1. A compound constructed by N (N is an integer of 2or more) kinds of phases containing at least one kind of elementselected from a group consisting of Co, Ti, V, Cr, Mn, Fe, Ni, Si, Pb,Bi and Al, wherein at least one kind (N−1) to kinds among said N kindsof phases are continuous phases, and the other phases are discontinuousphases.
 2. A compound according to claim 1, wherein a refractive indexof the compound changes in accordance with an incident light when theincident light-enters, and assuming that the refractive index is no at atime when no incident light enters and an intensity of the incidentlight is I, and an absolute value n of the refractive index to beobserved is represented by n=n₀+n₂I, a value of n₂ lies in a range ofgreater than 1.0×10⁻⁹ (m²/W) to less than 1.0×10⁻⁷ m²/W).
 3. A compoundaccording to claim 2, wherein the refractive index changes in a range ofgreater than 2.50×10⁻⁷ seconds to less than 3.50×10⁻⁷ seconds after theincident light enters, and the refractive index returns to an originallyset refractive index within a time interval in a range of greater than2.5×10⁻⁷ to less than 1.0×10⁻² after eliminating the incident light. 4.A compound according to claim 1, further comprising an oxide containinga Co oxide of 60 to 95 weight % as converted into an oxide of CoO and atleast one kind of element selected from a group consisting of Si, Ti,Al, Pb and Bi as a remaining part.